One function of footwear is to provide traction. Traction can help the wearer to change from a stationary state to a moving state (such as starting a race), to change from a moving state to a stationary state (such as stopping a slide on ice), or to change direction when moving (such as pivoting in a basketball game). Some circumstances need more traction, and specialized footwear has been created for those circumstances. For example, high-traction footwear with spikes, cleats, or other surface-engaging projections have been created, such as for playing certain sports and for walking on slippery surfaces.
Many types of footwear provide permanent surface-engaging projections. However, there are limitations to such footwear with permanent surface-engaging projections. For example, the wearer may walk on different types of surfaces. Permanent projections may be appropriate for some of these surfaces, but not others. These latter surfaces may damage the projections, or may be damaged by them. For example, spikes can damage a wood floor, or can be bent by a hard stone surface. There are also hard surfaces for which footwear with projections actually provides less traction than footwear without projections. Using footwear with permanent surface-engaging projections, the wearer generally must face the inconvenience of carrying different types of footwear and changing footwear to cross different surfaces.